For resin molded articles, it is commonly known that glass fibers, carbon fibers, mica, glass beads, glass flakes or the like are added as a filler to a matrix resin to achieve reduction in warping and deformation and/or improvement in mechanical strength. For such a resin molded product, it has been considered preferable to surface-treat the filler with a silane coupling agent or the like to improve the adhesion between the matrix resin and the filler and thereby further enhance the mechanical strength of the resin molded article.
For example, in relation to resin molded articles whose matrix resin includes a polyolefin such as polypropylene, various techniques for improving the adhesion between the matrix resin and a filler have been proposed. For example, Patent Literature 1 proposes using glass fibers as a filler for polyolefin reinforcement and surface-treating the glass fibers with a specific treatment agent to improve the adhesion between the glass fibers and a polyolefin used as a matrix resin. A treatment agent proposed in Patent Literature 1 contains an organofunctional inorganic coupling agent and a polyolefin compatible film forming polymer such as a carboxylic acid-modified polyolefin. Patent Literature 2 discloses using glass fibers as a filler for polyolefin reinforcement and treating the surface of the glass fibers with a treatment agent (sizing agent) containing an acid-modified polyolefin resin and a silane coupling agent to improve the adhesion between the glass fibers and a polyolefin resin used as a matrix resin. Patent Literature 3 discloses using carbon fibers as a filler and employing a modified polyolefin grafted with maleic anhydride and (meth)acrylic acid ester as an agent for surface-treating the carbon fibers to improve the adhesion between the carbon fibers and polypropylene used as a matrix resin.
Patent Literature 4 describes a technique that improves the adhesion between a filler and a matrix resin by the use of a specific resin (a resin including polypropylene and an epoxy-modified polyolefin) as the matrix resin rather than by surface treatment of the filler.